An alignment apparatus that aligns an optical fiber needs to not only perform alignment in the horizontal and vertical directions of a cross section of the optical fiber, but also align a rotation angle whose central axis is the longitudinal direction of the optical fiber. To align a rotation angle, some alignment apparatuses use active alignment, and some alignment apparatuses use passive alignment. Some alignment apparatuses using passive alignment perform alignment by observing an end face of an optical fiber, or by observing a side of an optical fiber by use of two markers on the orthogonal axis of the optical fiber.
Also, the technique of aligning an optical fiber having a core in its central portion, and the technique of aligning an optical fiber having two cores are published.